This invention relates to welding of precision-machined hollow bodies to other members, and particularly to welding tubular bodies of circular or rectangular or other cross sections, such as electronic waveguides, which have critical dimensions, to a coupling member such as a circular ring or fin or key and flange so that the precision bodies may ultimately be joined to each other.
For purposes of this application terms such as "precision tube bodies" or "tubular bodies" mean precision machined tubular bodies. The term "tubular" refers not only to bodies of circular cross section but also to rectangular and other cross sections. The bodies considered here are for use as waveguides, but may also be made for use in electronic machinery, tools, precision means and the like.
A circular waveguide generally transmits or propagates electromagnetic energy in the gigahertz band with wavelengths in the millimeter range. A circular waveguide has the disadvantage that small deformations or bending of the waveguide not only increase the attenuation and limit the signal being transmitted, but also easily change the transmitted wave from one mode to another. For this reason, circular waveguides must be manufactured to extreme accuracies within very low tolerances in the axial direction with respect to roundness, the longitudinal direction with respect to straightness, and with respect to smoothness at the inner face of the tube body. An extended conduit line of circular waveguides for long distance millimeter transmission can be formed by joining high precision tubular bodies having outside diameters of about 50 to 70 millimeters and wall thicknesses of about 2 to 5 millimeters. The mean radius of curvature of the tube axis along the inner face of the tube body is finished to within a degree for several hundred meters to several thousand meters and the roughness Hmax at the inner face of the tube is finished to a degree of several .mu.. However, tube bodies must be joined without impairing the characteristics of the overall tube. Such tube bodies are joined by coupling them to each other. However, they must be coupled in such a way so that when the tube body and coupling are welded, the strain at the inner face of the tube body due to the welding must be kept less than several 10.mu. at the most. Preferably it is desirable to keep the strain less than 10 to 15.mu. to avoid deterioration of the tube body and hence the signal.
Generally, a tube is welded to a metallic body by means of electric arc welding, such as TIG welding, MIG welding, or the like. In these processes, an electric arc is produced between a wire and the metal to be welded so as to weld both of them. This produces a large amount of heat in the welding area. This results in a broad melted area. However, the thermal effect of the arc over a wide portion, and the strains imparted by contraction of the molten metal upon solidification cause large deformations at the inner face of the tube body. Moreover, the welds and their thermal effect may cause deterioration of any substances coating the interior of the tubes. Such deterioration impairs the characteristics of the tube body substantially and causes it to lose utility.
Mechanical joining of tube bodies, such as by screwing parts to each other, caulking, and the like, avoid the effect of welding heat. However, such mechanical arrangements require work of extremely high accuracy and raise the costs of a system. In joining long tubes with couplings, seizure or the like at the screw portion may occur and deteriorate the operating properties of the tube. Thus mechanical joining has proved to be unprofitable and undesirable industrially.
The force necessary for caulking may impair the characteristics of the tube body. Mechanical coupling generally requires sealing to prevent leakage where gases are enclosed within the tube body and to prevent invasion of gas from the outside of the tube body. Generally, sealing by packing produces a poor quality seal compared with welding, particularly where the sealed members must be used for a long time such as several decades.
It is an object of this invention to provide a method for welding, whereby in the joint between a tube body and a metallic body, by the welding bead, which has restricted any strain due to welding in a range not to impair the characteristics of the tube body, the capacity of locking and the capacity of sealing of the joint are obtained at the same time, thus solving the problems of known method all together.
As is publicly known, new techniques such as electron beam, plasma, laser and the like have been recently developed and generally utilize the characteristics of high energy density, high thermal efficiency, without the need of a welding rod or core wire and the like; they are applied as far as the field where usual methods for welding is not applicable. The electron beam, plasma, or laser beam, form a concentrated heat-producing beam of energy.